Self-recognition or immune tolerance is mediated by several mechanisms including presentation of a “self” peptide to a CD4+ or CD8+ T cell, eliminating, inhibiting, or converting autoreactive (self-reactive) T cells that would potentially attack a cell producing the autoantigen (self-protein) from which the particular epitope (peptide) is derived. Autoimmune diseases such as Type 1 diabetes (T1D), rheumatoid arthritis (RA), multiple sclerosis (MS), psoriasis, systemic lupus erythematosus (SLE), and inflammatory bowel disease (IBD) can develop when this process is deficient or altered, and the immune system inappropriately attacks the body's own tissues. The National Institutes of Health estimates that 23.5 million Americans suffer from an autoimmune disease. Due to the complexity of these diseases (resulting from a combination of multiple genes and environmental factors), it has been difficult to apply drugs or biologics targeting one or a few pathways to restore tolerance efficiently and durably.
Current therapies for autoimmune disorders concentrate on symptomatic response and on mitigating the immune system as a whole, which has the inherent drawback of increasing susceptibility to infections and otherwise controlled malignancies. Antigen-specific therapy has recently emerged as a potential long-term solution to autoimmune disorders, but eliciting appropriate immune responses (i.e. tolerance-inducing or tolerogenic) and targeting sufficient numbers of disease-driving T cells has proven difficult. Immune tolerance, which prevents an immunogenic response from developing upon self-recognition, is mediated by several mechanisms, primarily involving the presentation of “self” peptides to CD4+ or CD8+ T cells in a manner that results in the elimination, inhibition, or conversion of the autoreactive T cells that otherwise would potentially attack cells and tissues that are the source of autoantigens and/or support the production by B cells of antibodies that react against these autoantigens. Under normal conditions (in absence of inflammation or infection), the presentation of epitopes (peptides or regions of a protein antigen that are recognized by immune cells) by specialized antigen-presenting cells (APCs) typically instructs the immune cells not to attack cells and tissues bearing these particular autoantigens. APCs that acquire antigens exogenously (from their milieu) more effectively engage CD4+ T cells, whereas those producing antigens endogenously present epitopes mainly to CD8+ T cells. However, both CD4+ and CD8+ self-reactive T cells should be silenced in order to prevent autoimmunity.
APCs include “professional” hematopoietic cells, primarily dendritic cells (DCs) but also macrophages and B cells, and “non-professional” non-hematopoietic cells, primarily lymph node stromal cells that have most contact with immune cells. Only professional APCs have the ability to elicit a productive immune response in the presence of recognized inflammatory signals and pathogen elements. Absent such signals, professional APCs tend to induce tolerance to presented antigens, while non-professional APCs, which do not upregulate the costimulatory ligands required for full activation are by default robustly tolerogenic. Stromal cells express lower MHC levels, and some do not express MHC class II (MHCII). They also have more limited endocytosis compared to professional antigens. Thus, stromal cells primarily present endogenously expressed antigens on MHC class I (MHCI), and a specific subset of epithelial cells in the thymus expresses high levels of MHCII and is able to present endogenous antigens on MHCII via autophagy.
Stromal Cells (SCs) are non-professional APCs that inherently lack the accessory molecules needed to stimulate effector T cell responses and have limited ability to acquire exogenous antigens and present them. Lymph node stromal cells (LNSCs) are constantly in contact with circulating T cells. They can present endogenously expressed peptides to naïve CD8+ T cells, leading to their deletion or anergy (Cohen, et al. J Exp Med 207: 681-688; Fletcher et al. (2010), J Exp Med 207: 689-697; and Cire, et al. (2016) Mol Ther.). They also participate in the maintenance of Tregs (Baptista et al. (2014) eLife 3) although their MHC-II expression is limited to some subsets or transferred from DCs (Dubrot et al. (2014), J Exp Med 211: 1153-1166). SCs and parenchymal cells are more readily transfected by DNA vaccines and other non-viral vectors than DCs (Yin et al. (2014), Nature reviews Genetics 15: 541-555.). After the death of SCs, a limited quantity of antigens may be passed onto DCs, but the majority of endogenously expressed antigens are only presented as peptides on MHC-I to CD8+ T cells. Indeed, DNA vaccines can lead to a reduction of antigen-specific CD8+ T cells in T1D patients and delayed loss of C-peptide secretion without notable adverse effect (Roep et al. (2013), Science translational medicine 5: 191ra182). However, engagement of CD4+ T cells by endogenous antigens expressed from DNA vaccines is inefficient. When targeted to MHC-II using a lysosome-targeting signal, a single endogenously expressed peptide allowed engagement of diabetogenic CD4+ T cells and reduce disease incidence (Rivas et al. (2011) J Immunol 186: 4078-4087). However, multiple treatments (≥3) were required to achieve a measurable immunological response, yet without evidence for antigen-specific Treg induction (Rivas et al. 2011). Although antigen-specific immunotherapy (ASIT) using a single antigen or epitope may achieve partial protection, they are likely not as effective as if diabetogenic T cells specific to multiple β cell Antigens (involved via epitope spreading) were targeted. Furthermore, MHC-II is absent or very low on most SC subsets, which restricts direct presentation to CD4+ T cells. While SCs do not readily migrate to the draining lymph nodes to engage T cells, there are reports of stromal cells trafficking from the peritoneum or adjacent adipose tissue into the local lymph nodes (Jalili et al. (2016) PloS one 11: e0146970; and Benezech et al. (2012) Immunity 37: 721-734).
Current antigen-specific therapies use either exogenously provided whole antigens or peptides delivered orally, intranasally or intravenously, which tend to be mostly processed onto major histocompatibility (MHC) class II molecules (MHCII) and presented as peptides to CD4+ T cells, or endogenously expressed proteins or peptides delivered by injection of DNA plasmids or viral vectors, which results mainly in MHC class I (MHCI) presentation to CD8+ T cells. These strategies, which cause the antigen to be presented primarily on MHCII (to CD4+ T cells) or on MHCI (to CD8+ T cells), have met with limited success.
A strategy and method for eliciting a broad tolerogenic response in autoreactive (self-reactive) T cells using antigen-specific therapy, which specifically targets the pathogenic T cells to modulate or prevent autoimmune disorders is needed in the art. The invention described herein addresses these needs.